TAMR is expected to be one of the future generations of magnetic recording technologies that will enable recording at ˜1-10 Tb/in2 data densities. TAMR involves raising the temperature of a small region of the magnetic medium to near its Curie temperature where both of its coercivity and anisotropy are significantly reduced so that magnetic writing becomes easier to achieve even with weak write fields characteristic of small write heads in high recording density schemes. In TAMR, optical power from a light source is converted into localized heating in a recording medium during a write process to temporarily reduce the field needed to switch the magnetizations of the medium grains. Thus, with a sharp temperature gradient of TAMR acting alone or in alignment with a high magnetic field gradient, data storage density can be further improved with respect to current state of the art recording technology.
In addition to the components of conventional write heads, a TAMR head also typically includes an optical waveguide (WG) and a plasmon antenna (PA) or plasmon generator (PG). The waveguide serves as an intermediate path to guide external laser light from a source mounted on a back side of the slider to the PA or PG where the light optical mode couples to the local plasmon mode of the PA or to the propagating surface plasmon (SP) mode of the PG. After the optical energy is transformed to plasmon energy, either with local plasmon excitation in the PA or with energy transmission along the PG, it is concentrated at the medium location where heating is desired. Ideally, the heating spot is correctly aligned with the magnetic field from the write head to realize optimum TAMR performance.
However, in the prior art, alignment of the heated spot with the magnetic field from the write head on the magnetic medium has been difficult to achieve. Spot size is typically around 100 nm or greater which is significantly larger than the <50 nm size needed to make the first generation of TAMR devices with high optical efficiency.
Current technology encompasses a TAMR head structure that integrates an edge plasmon generator (EPG) with a triangular shape from a cross-sectional view. The shape edge of the triangular EPG is placed in the vicinity of an optical waveguide and supports a very confined edge plasmon mode. Through evanescent coupling, the optical energy in the WG can be efficiently transferred to EPG mode. The EPG transmits the plasmon energy toward the air bearing surface (ABS) and focuses the energy at a spot on the medium located underneath the EPG. Local confinement of the edge plasmon mode is determined by the angle that forms the EPG shape edge, the radius of the triangle corner, the noble metal composition of the EPG, and the dielectric material surrounding the tip. For a 25 nm tip radius, optical spot size in the medium is about 100 nm in full-width half maximum.
By using a plasmon shield formed proximate to the EPG tip at the ABS as we disclosed in U.S. Pat. No. 8,036,069, the optical spot on the medium can be further reduced. The optical spot size with a plasmon shield is related to the gap distance between EPG and plasmon shield and can be reduced to 50 nm with a gap distance less than 40 nm, for example. Although the optical spot size may be reduced to a range of 20-30 nm with a 10 nm gap distance, the optical efficiency is significantly lowered which requires a higher laser power. However, higher laser power is not desirable for various reasons including reliability concerns.
A better choice to obtain small and scalable optical spot size is to incorporate an isolated metallic feature called a peg at an end of a PG at the ABS. We have disclosed one example of a peg in US Patent Application 2013/0148485 that is described in more detail in a later section. At the ABS, the SP mode is confined around the free standing peg, and heats the media locally while the recording head flies over the media surface. Confinement of optical energy at the media surface depends on the peg dimensions, the spacing between the ABS and magnetic medium recording layer, and the thermal properties of the media layers. Therefore, optical spot size may be scaled down by fabricating a smaller peg surface area at the ABS. Although noble metals such as Au, Ag, and Cu and their alloys are often selected as the peg material, there is a corrosion issue with Ag and Cu when they are exposed to air. Furthermore Au is associated with a migration issue at temperatures well below its melting point. As a result, a PG with a peg portion made from a noble metal exhibits poor reliability during recording tests.
Other PG with different compositions are being developed. However, current technology does not provide a TAMR structure with a PG that allows for a narrow optical spot size of around 20 nm or less with good reliability, especially when the PG including the peg portion comprises Au or similar noble metals with high optical efficiency and low resistive heating. Therefore, a plasmon generator with an improved design is needed to enable high efficiency of optical energy transmission to the ABS, scalable spot size, and acceptable reliability.